1. Field of the Invention
The present invention relates generally to a thin-film magnetic head and, more specifically, the present invention relates to an MR-inductive composite type thin-film magnetic head that is integrally equipped with an inductive head used for recording and a magneto-resistive head (MR head) used for playback.
2. Background Information
Devices such as computers and word processors, etc., are now widely used in Japanese industry, and the magnetic memories contained in such devices have continued to increase in capacity. Furthermore, as the capacity of such magnetic memories has increased, there has been a need to improve the recording and playback performance of thin-film magnetic heads.
Under such conditions, composite type thin-film magnetic heads which are integrally equipped with an inductive head used for recording and a magneto-resistive head (MR head) used for playback have been proposed for use in place of conventional inductive heads.
The layer composition of a composite type thin-film magnetic head 1 is as shown in FIGS. 1, 2 and 3. That is, in such a head, an inductive head used for recording and a magneto-resistive head used for playback are laminated into an integral unit.
Specifically, in such a composite type thin-film magnetic head, an inductive head used for recording is formed by the upper portion shown as the portion indicated by bracket A in FIG. 3. Furthermore, a magneto-resistive element 5 is contained in the lower layers, so that a magneto-resistive head B is formed by this portion.
The respective layers will be described below.
The above-mentioned composite type thin-film magnetic head 1 uses a substrate 6 consisting of a ceramic such as Al.sub.2 O.sub.3, etc., as a base, and an insulating film 7 consisting of Al.sub.2 O.sub.3 is formed on the surface of this substrate 6. Furthermore, a lower shielding magnetic film 8 is laminated on the surface of this insulating film 7. Moreover, a magneto-resistive element 5 is embedded in this lower shielding magnetic film 8.
The magneto-resistive element 5 is a member which has a type of current-magnetic effect, and shows a change in electrical resistance as a result of the magnetization of the material. Materials which show a magneto-resistive effect include NiFe, NiFeCo, NiCo, FeMn, Fe.sub.3 O.sub.4, CoPt/Cr and Fe/Cr, etc. The appropriate material of the magneto-resistive element 5 is selected from this set of materials.
An upper shielding magnetic film 10 is formed on top of the magneto-resistive element 5. This upper shielding magnetic film 10 is laminated over more or less the entire area of the substrate 6.
A magnetic gap film 11 is present on top of the upper shielding magnetic film 10, and a recording inductive magnetic film 12 is laminated so that this magnetic gap film 11 is sandwiched between said recording inductive magnetic film 12 and the upper shielding magnetic film 10. Furthermore, a protective layer 18 is formed on top of the recording inductive magnetic film 12.
The shapes of the magnetic gap film 11 and recording inductive magnetic film 12 as seen in a plan view are shown in FIG. 1. The front-end portions (where the magnetic gap is formed) are narrow, and the area is somewhat larger on the inside. Furthermore, as is shown in FIGS. 1 and 2, the recording inductive magnetic film 12 is separated from the upper shielding magnetic film 10 and magnetic gap film 11 on the inside of the composite thin-film magnetic head 1, and an insulating film 14, conductive coil film 15 and insulating film 16 are interposed between the upper shielding magnetic film 10 and recording inductive magnetic film 12. Furthermore, the upper shielding magnetic film 10 and recording inductive magnetic film 12 are coupled in the area of a rear gap 20 located to the rear, and the conductive coil film 15 is installed in the form of a coil centered on this rear gap 20.
Meanwhile, the upper shielding magnetic film 10 and the front-end portion of the recording inductive magnetic film 12 face each other across the magnetic gap film 11, so that a magnetic gap is formed in this area.
In the above-mentioned composite type thin-film magnetic head 1, the upper shielding magnetic film 10 functions as a magnetic shield which protects the magneto-resistive element 5 from the magnetic effects of the inductive head A used for recording which is laminated on top of said upper shielding magnetic film 10, and also functions as one of the cores of the inductive head.
Accordingly, in the upper shielding magnetic film of the prior art, a magnetic material which is the same as the material of the core of a conventional inductive head is used as the material of the upper shielding magnetic film.
In specific terms, in the above-mentioned conventional composite type thin-film magnetic head 1, magnetic films consisting of permalloy (Ni--Fe) are used as the upper shielding magnetic film 10 and recording inductive magnetic film 12. Furthermore, the above-mentioned upper shielding magnetic film 10 and recording inductive magnetic film 12 consisting of permalloy are formed by electroplating. Moreover, in the prior art, the concentrations (compositions) of these magnetic films are both fixed, and are uniform in all portions of the films.
Specifically, in the above-mentioned conventional composite type thin-film magnetic head 1, films formed by forming a nickel-iron alloy (permalloy) into a film are used as the magnetic films, and the compositions of the respective films are uniform in all portions of the films. Accordingly, in the conventional composite type thin-film magnetic head 1, the saturation flux density (B.sub.s) and magnetic permeability (.mu.) of the magnetic films are the same at all points in the films.
Furthermore, in regard to the composition of the permalloy magnetic films used in the conventional composite type thin-film magnetic head 1, a composition containing 81 to 83 wt % Ni has been considered optimal.
During recording, the composite type thin-film magnetic head 1 operates as follows. A signal current is applied to the conductive coil 15 so that a magnetic flux is generated in the magnetic gap between the tip end portions of the recording inductive magnetic film 12 and the upper shielding magnetic film 10. As a result, the signal is written on a magnetic medium 22.
During playback, the magnetic flux from the magnetic medium 22 passes through the area between the lower shielding magnetic film 8 and the upper shielding magnetic film 10 with the same timing as the passage of the magnetization transition regions. Accordingly, the resistance of the magneto-resistive element 5 located between the lower shielding magnetic film 8 and the upper shielding magnetic film 10 varies according to the variation in the magnetic flux in this case, so that a playback signal is output.
The above-mentioned composite type thin-film magnetic head 1 has a structure in which the head used for recording and the head used for playback are separate. Superior recording characteristics and a playback output with a higher resolution (compared to the characteristics of a conventional inductive head) are obtained by respectively optimizing the recording head and playback head.
However, the capacity of magnetic memories used in recent computers, etc., has been increasing at an accelerated rate. Accordingly, there is a need for composite type thin-film magnetic heads with even more superior recording characteristics and resolution.
Here, in the case of inductive heads, it is known that the recording characteristics of the head improve with an increase in the saturation flux density (B.sub.s) of the magnetic films forming the core. Furthermore, in the case of permalloy, it is known that the saturation flux density (B.sub.s) increases with a decrease in the nickel content. On the other hand, however, when the nickel content of permalloy is decreased, the magnetostriction constant increases so that the playback performance becomes unstable. Conventionally, therefore, permalloy containing 81 to 83 wt % Ni, which shows a good balance between saturation flux density (B.sub.s) and magnetostriction constant, has been considered optimal for magnetic films used in heads.
On the other hand, in the case of the above-mentioned composite type thin-film magnetic head 1, the inductive head is used only for recording, with playback being accomplished by means of the above-mentioned magneto-resistive head. Accordingly, a drop in the playback performance of the inductive head which is secondarily generated as a result of an increase in the saturation flux density (B.sub.s) of the magnetic films is not a problem.
However, in the above-mentioned composite type thin-film magnetic head 1, as was described above, one of the magnetic films must function both as a core and as a magnetic shield. Furthermore, for this magnetic film to exhibit a sufficient level of functioning as a magnetic shield, it is desirable that the saturation flux density (B.sub.s) of said film be low. Accordingly, in the above-mentioned composite type thin-film magnetic head 1 as well, there is an upper limit to the saturation flux density (B.sub.s) of the magnetic films, so that satisfactory recording characteristics cannot be obtained.
Therefore, it is desired to allow the use of films with a high saturation flux density (B.sub.s) as the above-mentioned magnetic films, and to develop a composite type thin-film magnetic head which has both superior recording characteristics and high resolution.